Among the existing pre-treatment methods, torrefaction is used to achieve reasonable rates and yields during enzyme hydrolysis of biomass. On the other hand, the presence of furan and phenol compound is unavoidable and must be taken into consideration in order to minimize the potential negative effects on the fermentation steps. The present study evaluated the hot water extraction method for the removal of fermentation inhibitory compounds from torrefied biomass.
Torrefaction was carried out at a temperature of 220°C with residence times of 3 min. The dry and torrefied wood was subjected to a process of hot water extraction, that was carried out at a temperature of 80°C for 4 hours to maintain a water/wood ratio of 20:1 (mass/mass). The chemical composition of torrefied wood was analyzed using gas chromatography-mass spectrometry (GC-MS).
Based on the GC-MS analysis, it was confirmed that the main components of torrefied wood were 5-methyl-2-furancarboxaldehyde, 4-methoxyphenol, 2,5-furandicarboxaldehyde, 4-ethyl-1,3-benzenediol, 3-hydroxy-4-methylbenzaldehyde, 2-methoxy-4-vinylphenol, vanillin, and syringol, which were primarily derived from lignin depolymerization. Furan and phenol compounds were significantly reduced in the solid residue of the torrefied wood that was treated with hot water than that in the torrefied wood chip. Also, the furan and phenol content in the liquid (from the torrefied wood) was higher than that in the solid residue of the torrefied wood, which was subjected to the hot water extraction method. Therefore, hot water extraction method after torrefaction can also be used avoided by reducing the byproduct for removal of fermentation inhibitory compounds.